Pilot data, providing the basis for a recent publication, demonstrates that oxytocin administered intracerebroventricularly into virgin female rats induces rapid onset full maternal behavior. This phenomenon has been shown to be the estrogen-dependent. The incidence of maternal response is dose related. Specificity studies involving a large number of peptides and steroids has shown that oxytocin is the most potent maternogenic hormone but that both (Arg8) vasopressin and luteinizing hormone-releasing hormone induce a significant rate of full maternal response as well. We propose to pursue fundamental behavioral and pharmacological questions that flow from our original discovery and pilot data. We intend to quantitatively compare peptide-induced maternal behaviors with postpartum maternal behavior and with each other. In addition, an investigation of the functional relationship between the three principal maternogenic peptides will be undertaken. Since luteinizing hormone-releasing hormone has been shown to induce lordosis behavior in female rats we are also curious about the possible efficacy of oxytocin and (Arg8) vasopressin in this experimental paradigm. We also intend to determine the maternogenic efficacy of peptides in male rats. The behavioral studies will be based on methods devised by ourselves or other workers in the field. In some experiments subeffective doses of oxytocin, (Arg8) vasopressin, or luteinizing hormone-releasing hormone will be used to determine whether they increase the behavioral efficacy of the two other peptides. Specific antibodies against each of these peptides will be used to determine the primary behaviorally active peptide(s) initiating postpartum maternal behavior.